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What is Progesterone?

Although progesterone is found in both males and females, it is primarily known for its role in conception, pregnancy, and the regulation of a woman’s menstrual cycle. Produced in the ovaries, adrenal glands, and the placenta of pregnant women, progesterone has several functions in addition to its role as a sex hormone. It supports bone density, protects against the proliferation of breast and uterine cells, and acts as a coating for the nerve fibers of the brain, reducing hyperexcitability. A female’s progesterone levels rise and fall according to the stages of her life. While men also synthesize a small amount of this hormone, it is much less important than testosterone when it comes to sexual maturity. Synthetic forms of progesterone (progestins) are widely used in birth control pills and hormone replacement therapy.

Natural progesterone levels are suppressed in women who take synthetic forms, so blood tests are inaccurate in these case. Otherwise, a blood test is usually administered twenty-one days after the start of a woman’s period, if she is still menstruating. Because progesterone readings normally fluctuate in women, there are a number of normal ranges for this hormone, as shown here:

PROGESTERONE LEVELS

SEX

ng/ml

nmol/l

Females

Follicular phase

0.2-1.4

0.64 – 4.45

Luteal phase

4 – 25

12.7 – 79.5

Post-Menopausal

0.1 – 1

0.32 – 3.18

Males

0.1 – 1

0.32 – 3.18

Conversion factor: 1 ng/ml = 3.18 nmol/l

While variations in progesterone levels may be perfectly normal, sometimes a high reading is cause for further testing.